• Applied Chemistry for Engineering
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• v.29 no.5
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• pp.571-580
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• 2018

In this study, hybrid adsorbents (SS) were prepared by mixing spent coffee grounds (SCG) and sericite, a kind of clay minerals, to adsorb Pb(II) from an aqueous solution. In FT-IR analyses, the main functional groups of SS adsorbents were O-H, C=O and C-N groups. The specific surface area, cation exchange capacity and the pore diameter of SS were larger than those of using SCG and sericite. Formation conditions of the SS adsorbent were the optimum pyrolysis temperature of $300^{\circ}C$, SCG : sericite ratio of 8 : 2, and particle size of 0.3 mm. Langmuir adsorption isotherm was more suitable than Freundlich one, and the maximum adsorption capacity was reached 44.42 mg/g. As a result of the adsorption thermodynamic analysis, the adsorption of Pb(II) onto SS was the physical adsorption and exothermic process in nature. The regeneration of SS adsorbent using distilled water showed 88~92% recovery and the active site of SS adsorbent decreased with increasing the reuse cycle time. As a result, SS adsorbent showed that it can be used to remove Pb(II) easily, inexpensively and efficiently without any pre-treatment from aqueous solutions.

• Journal of the Korean Society of Marine Environment & Safety
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• v.22 no.1
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• pp.138-144
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• 2016

Titanium is resistant to general corrosion and in sea water because of the passivity layer film on the surface of material, but may be attacked by environments that cause breakdown of the protective oxide layer including hydrochloric, sulfuric and phosphoric acids. In this study, the Ti alloys were solution heat treatment 5hours at $1066^{\circ}C$ and $966^{\circ}C$, and followed by aging heat treated, 1, 4, 8 and 16 hours in $500^{\circ}C$, $600^{\circ}C$ and $650^{\circ}C$ respectively. The heat treated specimens were measured micro Vicker's hardness, and then accomplished electrochemical polarization test for comparing corrosion in 1N sulfuric acid solution. Additionally, micro structures were taken for corrosion tested specimens. The results showed that corrosion resistance was higher in solution heat treated alloy than base and age heat treated metal. Measured corrosion resistants were increased as increasing aging heat treatment time and temperature.

• Journal of Welding and Joining
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• v.32 no.3
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• pp.95-101
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• 2014

Joining of grey cast iron by fusion welding has much difficulties for its extremely low ductility and low toughness because of the flake form of the graphite. And the brittle microstructure, i.e. ledeburite may be formed during fusion welding by its rapid cooling rates. By these kinds of welding problem, preheat and post heat treatment temperature must be increased to avoid weld crack or welding problems. In order to avoid these fusion welding problem, friction welding of cast iron was carried out for improving joint soundness, establishing friction welding variables. There is no factor for evaluating friction weldability in continuous drive type friction welding. In this point of view, this study proposed the parameters for calculating friction weld heat input. The results obtained are as follows ; 1. There was a close relationship between tensile strength and flash appearance of friction welded joint. 2. Tensile strength was decreased and flash was severely oxidized as increasing frictional heating time. 3. As increased forging pressure $P_2$, flash had a large crack and tensile strength was decreased. 4. As powdered graphite by rotational frictional force induced flat surface and hindered plastic flow of metal, tensile strength of welded joint was decreased. 5. Heat input for continuous drive type friction welding could be calculated by the factors of $P_1$, $P_2$ and upset distance(${\delta}$).

• Journal of Ocean Engineering and Technology
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• v.22 no.6
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• pp.75-82
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• 2008

Flame bending has been extensively used in the shipbuilding industry for hull plate forming In flame bending it is difficult to obtain the desired shape because the residual deformation dependson the complex temperature distribution and the thermal plastic strain. Mechanical bending such as reconfigurable press forming multi-point press forming or die-less forming has been found to improve the automation of hull plateforming because it can more accurately control the desired shape than line heating. Multi-point forming is a process in which external forces are used to form metal work-pieces. Therefore it can be a flexible and efficient forming technique. This paper presents an optimal approach to determining the press-stroke for multi-point press forming of curved shapes. An integrated configuration of Finite element analysis (FEA) and spring-back compensation algorithm is developed to calculate the strokes of the multi-point press. Not only spring-back is modeled by elastic plastic shell elements but also an iterative algorithm to compensate the spring-back is applied to adjust the amount of pressing stroke. An iterative displacement adjustment (IDA) method is applied by integration of the FEA procedure and the spring-back compensation work. Shape deviation between the desired surface and deform￡d plate is minimized by the IDA algorithm.

• Fire Science and Engineering
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• v.19 no.1 s.57
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• pp.93-98
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• 2005

The purpose of this paper is to judge the damage cause of instrument transformer(MOF; Metering Out Fit) installed in 22.9kV power receiving system. In the three-dimensional analysis of the restored MOF, the damage pattern progressed from inside to outside, there was no damaged part in the upside. The resistance of the carbonized middle part is roughly $100\kappa\Omega$ and the exothermic temperature at inside is presumed as about $300\~800^{\circ}C$ in the result of metallurgical structure analysis. The structure and the composition rate on metal surface by SEM is similar. In the result of FT-IR analysis, we can observe the absorbtion peak at $1500cm^{-1}\;and\;1730 cm^{-1}$ is small. The high exothermic peak showed at the center part of the coil in the result of DTA.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.487-487
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• 2011

Recently graphene has emerged as a fascinating 2D system in condensed-matter physics as well as a new material for the development of nanotechnology. The unusual electronic band structure of graphene allows it to exhibit a strong ambipolar electric field effect with high mobility. These properties lead to the possibility of its application in high-performance transparent conducting films (TCFs). Compared to indium tin oxide (ITO) electrodes, which have a typical sheet resistance of ${\sim}60{\Omega}$/sq and ~85 % transmittance in the visible range (400?900 nm), the CVD-grown graphene electrodes have a higher/flatter transmittance in the visible to IR region and are more robust under bending. Nevertheless, the lowest sheet resistance of the currently available CVD graphene electrodes is higher than that of ITO. Here, we report an ingenious strategy, irradiation of MeV electron beam (e-beam) at room temperature under ambient condition, for obtaining size-homogeneous gold nanoparticle decorated on graphene. The nano-particlization promoted by MeV e-beam irradiation was investigated by transmission electron microscopy, electron energy loss spectroscopy elemental mapping, and energy dispersive X-ray spectroscopy. These results clearly revealed that gold nanoparticle with 10 ~ 15 nm in mean size were decorated along the surface of the graphene after 1.5 MeV-e-beam irradiation. A chemical transformation and charge transfer for the metal gold nanoparticle were systematically explored by X-ray photoelectron spectroscopy and Raman spectroscopy. This approach advances the numerous applications of graphene films as transparent conducting electrodes.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.08a
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• pp.388-388
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• 2011

Graphene, with its unique physical and structural properties, has recently become a proving ground for various physical phenomena, and is a promising candidate for a variety of electronic device and flexible display applications. The physical properties of graphene depend directly on the thickness. These properties lead to the possibility of its application in high-performance transparent conducting films (TCFs). Compared to indium tin oxide (ITO) electrodes, which have a typical sheet resistance of ~60 ${\Omega}/sq$ and ~85% transmittance in the visible range, the chemical vapor deposition (CVD) synthesized graphene electrodes have a higher transmittance in the visible to IR region and are more robust under bending. Nevertheless, the lowest sheet resistance of the currently available CVD graphene electrodes is higher than that of ITO. Here, we report an ingenious strategy, irradiation of MeV electron beam (e-beam) at room temperature under ambient condition,for obtaining size-homogeneous gold nanoparticle decorated on graphene. The nano-particlization promoted by MeV e-beam irradiation was investigated by transmission electron microscopy, electron energy loss spectroscopy elemental mapping, and energy dispersive X-ray spectroscopy. These results clearly revealed that gold nanoparticle with 10~15 nm in mean size were decorated along the surface of the graphene after 1.0 MeV-e-beam irradiation. The fabrication high-performance TCF with optimized doping condition showed a sheet resistance of ~150 ${\Omega}/sq$ at 94% transmittance. A chemical transformation and charge transfer for the metal gold nanoparticle were systematically explored by X-ray photoelectron spectroscopy and Raman spectroscopy. This approach advances the numerous applications of graphene films as transparent conducting electrodes.

• Economic and Environmental Geology
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• v.24 no.2
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• pp.107-129
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• 1991

The Yonghwa gold-silver deposits are emplaced along $N15^{\circ}{\sim}25^{\circ}W$ trending fissures in middle Cretaceous porphyritic granite or Precambrian Sobaegsan gneiss complex. The results of paragenetic studies suggest that vein filling can be subdivided into four identifiable stages; state I: the main sulfide stage, characterized by base-metal sulfide minerals, iron oxides and minor electrum, stage II: electrum stage, stage III: electrum and silver-bearing sulfosalts stage, stage IV: post ore stage of carbonates and quartz. The ore mineralogy suggests that depositional temperature of the formation of the gold and silver minerals are estimated as 200 to $250^{\circ}C$ and 140 to $180^{\circ}C$, respectively. Sulfur fugacity of the formation of the gold and silver minerals are estimated as $10^{-14.0}$ to $10^{-12.2}$ atm and $10^{-18.5}$ to $10^{-17.2}$ atm, respectively. A consideration of the pressure regime during ore deposition bases on the fluid inclusion evidence of boiling suggests lithostatic pressure of less than 180 bars. This range of pressure indicate that vein system lay at depth of 700m below the surface at the time during mineralization. Salinities of ore-bearing fluids range from 0.4 to 6.9 wt.% equivalent NaCl. The sulfur and carbon isotopic data reveal that these elements were probably derived from a deep-seated source. The ${\delta}^{18}O$ of the hydrothermal fluid was determined from ${\delta}^{18}O$ values of quartz and calcite. Oxygen and hydrogen isotopic studies reveal that meteoric water dominate over ore-bearing fluid.

• Restorative Dentistry and Endodontics
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• v.18 no.2
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• pp.431-445
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• 1993

The purpose of this study was to observe corrosion characteristics of six dental amalgams and was to analyse corrosion products electrochemically. After each amalgam alloy and Hg was triturated as the direction of the manufacturer by using mechanical amalgamator, the triturated mass was inserted into the cylinderical metal mold ($12{\times}10mm$) and was condensed with 160kg/$cm^2$ by using the hydrolic press. The specimen was removed from the mold and was stored at room temperature for 1 week, and was polished with amalgam polishing kit. The anodic and cathodic polarization curve was obtained by using cyclic voltammetric method with 3-electrode potentiostat in saline for each amalgam and Ag, Sn, Cu plate specimen at $37{\pm}0.5^{\circ}C$. The potential sweep range was -1.7V~0. 4V(vs SCE) in working electrode and scan rate was 50mV/s and the exposed surface area of each specimen to the electrolytic solution was $0.79cm^2$. The results were as follows. 1. In anodic-cathodic polarization curve of amalgam specimens, two anodic current rising areas and two cathodic current peaks were obtained at the low Cu amalgam(CF, CS) specimen and three anodic current rising areas and three cathodic current peaks were obtained at the high Cu amalgam (TY, DS, HV) specimen. 2. As this compared with the anodic and cathodic current peak potentials of Sn, Cu and Ag specimen, the first cathodic current peak I c was caused by the reduction of divalent tin salt, second cathodic current peak IIIc results from the reduction of quadravalent tin salt, and third cathodic current peak me results from the reduction of copper salt. 3. As reverse potential sweeping was done repeatedly, anodic current was decreased slightly in all amalgam specimens.

• Journal of the Korean Chemical Society
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• v.47 no.6
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• pp.608-613
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• 2003

In order to remove particles on surface of post-oxide CMP wafer, new cleaning solution was prepared by mixing with DHF (Diluted HF), nonionic surfactant PAAE (Polyoxyethylene Alkyl Aryl Ether), DMSO (Dimethylsulfoxide) and D.I.W.. Silicone wafers were intentionally contaminated by silica, alumina and PSL (polystylene latex) which had different zeta potentials in cleaning solution. This cleaning solution under megasonic irradiation could remove particles and metals simultaneously at room temperature in contrast to traditional AMP (mixture of $NH_4OH,\;H_2O_2$ and D.I.W) without any side effects such as increasing of microroughness, metal line corrosion and deposition of organic contaminants. This suggests that this cleaning solution would be useful future application with copper CMP in brush cleaning process as well as traditional post CMP cleaning process.